DE69937467T2 - Multi-carrier transmission system with low power sleep mode and fast turn-on capability - Google Patents

Description

GENERAL PRIOR ART

The The invention relates to multicarrier transmission systems and includes a method and apparatus for establishing a power management sleep state in a multi-carrier system.

SUMMARY OF THE INVENTION

Multicarrier transmission systems provide fast data connections between communication points ready. Such systems have recently been used for communication over the Locals connection introduced connects a telephone service subscriber to a central office; In this important application, they are commonly referred to as "xDSL" systems denotes, wherein the "x" a certain variant the communication of the DSL (digital subscriber line), z. B. ADSL (asynchronous digital subscriber line), HDSL (fast digital subscriber line) etc. These become generic here simply referred to as "DSL" systems. In such systems, two transceivers communicate with each other Splitting the total bandwidth of the channel, the participant and the switch connects into a large number of separate subchannels, respectively with limited bandwidth operating in parallel. For example shares a common one System the subscriber connection channel in two hundred and fifty-six subchannels each of four kilohertz bandwidth. A first group of these (for example, one hundred and ninety - six) will be the communication of the Assigned to the subscriber (this is known as the "downstream" direction); a second Group (for example, fifty-five) the communication from the subscriber to the exchange assigned (this is known as the "upstream signal"). The remaining subchannels will be allocated to administrative, control and overhead functions.

About the Connection to be transmitted Data is divided into groups of bits (one group for each Subchannel). The set of bits allocated to a given subchannel gets on a carrier modulated its frequency for this channel is specific. As a rule, quadrature amplitude modulation is used for this purpose (QAM) is used, and the group of bits is mapped to a vector, which is defined by one of the points of a "constellation" that defines the allowed data points for transmission over this Subchannel specified at a given time. Every vector or data point thus a unique symbol representing a specific bit configuration for the transmission as a group over represents its associated subchannel. While of for the transfer of a symbol assigned period (commonly referred to as "symbol period" or "frame") transmits each subchannel its symbol in parallel with all other subchannels, so that in each frame large quantities transferred to data can be.

The guided by a symbol Number of bits depends from the properties of the subchannel over which it is to be transmitted. These can from vary from one subchannel to another. The main decision factor is the signal to noise ratio of the subchannel. Consequently, this parameter becomes measured from time to time to determine its value for each subchannel and thus the number of at a given time on the particular subchannel to be transferred To determine bits.

On the telephone channel, several impairments occur, which compensates have to be around a reliable transmission sure. In general, phase (delay) distortion of the transmitted Signals the strongest restrictive of these impairments. This distortion is frequency dependent and thus become components of a signal with different frequencies around varying amounts shifted, which distorts the signal and the probability a false detection is increased, if no precautions are taken to counteract it. For this purpose are usually Equalizer for Frequency (FDQ) and time delay (TDQ) in the transmission channel integrated to the phase (time) delay over the channel frequency band too equalize.

It also disfigure other impairments. For example, impaired a frequency-dependent signal attenuation the signal transmission on the phone line. This is done by using gain equalizers compensated on the line. Echoes on the wire are going through Use of echo cancelers treated, and phase and frequency offsets, for example, by the use of frequency division multiplexing in the telephone system can arise have to also be corrected.

The problem of signal degradation is particularly important in the xDSL configurations, which route the DSL broadcasts on a common line with ordinary voice communications, but do not use a splitter either at the subscriber premises or in the central office or at both locations. A "splitter" is, in principle, a filter that separates the low frequency voice transmissions (eg, from zero to four kilohertz) from the higher frequency data transmissions (which may extend into the megahertz band) and provides a high degree of isolation between the two. If a branching is missing, unique measures must be taken to set up voice and data communication to enable the same line. A more detailed description of the problem and its solution can be found in the co-pending application of Richard Gross et al. titled "Splitterless Multicarrier Modem", WO-A-9920027 , published April 22, 1999, assigned to the assignee of the present invention.

Because of their extensive use in Internet communications and other applications, DSL transceivers are usually kept "on" and ready to send or receive once installed and initialized. Thus, such modems consume a significant amount of power even if they are not actively sending or receiving data. Both for environmental reasons and to extend the life of the equipment, it is generally desirable to limit this energy or power consumption. In addition, such modems may be implemented or integrated in whole or in part in computing devices, such as personal and business personal computers, and such computers increasingly include power-saving procedures. See for example that U.S. Patent No. 5,428,790 "Computer Power Management System", issued on 27. 6. 1995 on the application of LD Harper. Thus, it is desirable to provide an ADSL modem that can accommodate power saving procedures.

by virtue of the complexity DSL transceivers and the circumstances in which they must operate it is necessary to initialize them before sending and receiving data. This initialization includes u. a. Channel corrections such as "training" of the frequency and Time domain equalizer and the echo canceler; Setting the channel gains; Adjust of phase and frequency offsets; and the same. In addition, it includes that Measuring the signal to noise ratio of each of the subchannels, calculating the bit allocation table characteristics from any given transmission conditions and replacing these tables with other modems with those a given modem communicates. More detailed discussions of this Procedures can be found in the above-referenced Richard application Gross et al. These procedures can take ten to hundreds of seconds to complete. For a new installation is the needed Time without meaning. For an already working installation is the time required to initialize or reinitialize system after suspending operation However, with power savings in general unacceptable, as in the Usually desired that will Modem immediately responds to a service request.

Out EP 0473465 A1 there is known a power saving arrangement in a portable cellular telephone system. However, this document mentions no multi-carrier transmission.

A The object of the invention is therefore to provide a multi-carrier transmission system with a Sleep mode with low power or low power mode and a fast turn-on capability.

A The object of the invention is also to provide a multi-carrier transmission system for use in the case of digital subscriber line communication, that fast from a sleep mode or low power mode to a fully powered on Can switch state.

A Another object of the invention is the provision of a DSL system, which can be easily integrated into a computer, the a sleep mode with low power or low power mode and quickly return to full function.

The The above objects are at least partially achieved by a multi-carrier transceiver according to claim 1 or a method for sleeping with low power or energy saving solved according to claim 5. Preferred embodiments are the subject of dependent Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The The following description of the invention refers to the attached drawings. It demonstrate:

1 a block and line diagram of a multi-carrier transmission system according to the present invention; and

2 a flow chart of the operation of the present invention.

DETAILED DESCRIPTION OF ONE EMBODIMENT

In 1 owns a DSL transceiver 10 according to the present invention, a transmitter part 12 for sending data over a digital subscriber line 14 and a receiver part 16 for receiving data from the line. The transmitter part 12 is through an input buffer and converter 18 which receives a serial data string (eg binary digits) to be transmitted and the data into several pairs of complex valued symbols X _i and their conjugations X _Ni = X ^* _i , i = 0, 1, ... N implements. These pairs of symbols are sent to a Fast Fourier Inverse Transform (IFFT) 20 to provide real-time output signals x _j , j = 0, 1, ... N / 2-1. These in turn become in a parallel / se Riell converter 22 converted into serial form and then to be applied to a line driver 26 to a digital / analog converter 24 created. The converter may apply a cyclic prefix to the signals x _j to counteract inter-symbol interference caused by the transmission medium. The driver 26 can be a gain control part 26a for regulating the signal amplitude (and thus the power) applied to a communication channel such as a digital subscriber line 24 is created.

The IFFT 20 can be considered as a data modulator. The symbols X _i and their conjugates X _Ni correspond to data points which define signal vectors in a constellation set of Quadrature Amplitude Modulation (QAM). The converter 18 Forms the respective symbols from the input data using a bit allocation table (BAT) 28 which specifies, for each subchannel, the number of bits to be passed by the symbol transmitted via this subchannel and thus defines the data point to be associated with the symbol. This table is typically computed in the transceiver and sent to other transceivers with which the present transceiver communicates, thereby enabling them to decode the symbols they receive from the present transceiver.

The number of bits that each symbol carries is determined by the characteristics of the subchannel over which the symbol is to be transmitted, and more particularly by the signal to noise ratio of the subchannel. Procedures for this calculation are known. 1A shows an example of such a table, as in the transceiver 10 is formed and stored. Thus it can be determined that via the subchannel 50 symbol to be transmitted has an allocation of six bits; those of the subchannel 51 is six bits; those of the subchannel 52 seven bits, etc.

One clock 30 controls the timing of the operation of the transmitter 12 , It provides input signals for a controller 32 which controls the individual units of the transmitter. If there is a transceiver in an exchange, the clock is 30 usually a master clock that synchronizes a remote transceiver, such as at the customer site. In the case of a transceiver at the customer site, as shown here for illustrative purposes, the clock is derived from the master clock in the central office, as described in more detail below in connection with the receiver portion of the transceiver. A frame counter (FC) 36 is with the controller 32 and maintains or maintains a count of the number of frames of data that the transceiver transmits or receives. Last, there is a state memory (SM) associated with the controller 34 verbun is the, the state of the transceiver for reasons discussed in more detail below.

Now with reference to the receiver part 16 it is formed by: a line conditioner 50 ; an analogue to digital converter (ADC) 52 ; a serial / parallel converter 54 ; a part for fast Fourier transform (FFT) 56 ; a detector 58 ; and a parallel / serial converter 60 , The processing device 50 compensated by the line 14 introduced transmission distortions and usually contains a frequency domain equalizer (FDQ) 50a ; a time domain equalizer (TDQ) 50b ; and an echo canceler (EC) 50c next to other elements. The ADC 52 converts the received signal into digital form and sends it to the serial / parallel converter 54 at. The converter 54 removes any cyclic prefix that may have been appended to the signal before it was sent and applies the resulting signal to the FFT 56 which effectively "demodulates" the received signal. The output of the FFT is sent to the decoder 58 created in conjunction with a bank allocation table 62 restores the symbols X _i and the bits associated with them. The output signal of the detector 58 is sent to the parallel / serial converter 60 created, which restores the data stream that was originally created to the sender.

A phase locked loop (PLL) 62 , receives from the line conditioner 50 a timing reference signal sent by the transmitter with which it is communicating (e.g., the CO transceiver). The PLL 62 locks with this signal and controls a clock in sync with the master clock in the driving transmitter 64 at. The control of the receiver part is controlled by the controller 32 provided.

As already mentioned, For example, the transceiver of the present invention is commonly referred to in U.S. Pat integrated a computer such as a personal computer; indeed it can be implemented as an integral part of such a computer be a power saving or a low power mode that activates if the computer is not actively running. It is thus desirable, that the Transceiver is able to suspend its operation and in to enter a "sleep" mode, by consuming less electricity or energy or power when he does not for sending or receiving data is needed, but still in is able to resume sending or receiving almost instantaneously z. With a delay less than a second. This is in the present invention as follows reached.

As an illustration, the function Example of the invention explained via a transceiver, which is located at a customer site (referred to herein as the "CPE transceiver") that transmits data over the subscriber's data subscriber line to a transceiver located in the central office (here as the "CO Transceiver "). In particular, it will open 2 and 3 referred to in connection with this meeting. The shutdown operation of the CPE transceiver begins upon receipt of a shutdown command (step 80 ) by the CPE transceiver controller 32 , The shutdown command may be sent to the controller from an external source, such as a personal computer in which the transceiver is contained 32 be created; it may be a result of the monitoring of the input buffer in the transceiver itself 18 and the determination that no data has been applied to it for a given period of time; or it may be in response to a shutdown command from the CO transceiver.

Considering the first two cases for the moment, the CPE transceiver responds to the command by sending an "enter sleep" signal to the CO transceiver (step 82 ). The CO transceiver responds by sending a "confirm sleep mode" signal to the CPE transceiver (step 84 ). In addition, the CO transceiver sends a pilot tone to the CPE transceiver (step 86 ), which allows the CPE transceiver to maintain synchronization with the CO transceiver during sleep mode. More specifically, as in 1 shown the pilot tone from the line conditioner 50 to the PLL 62 created the local clock 64 synchronous with the master clock 30 in the CO transceiver drives. The beat 64 in turn controls the frame counter 66 synchronous with the frame counter 36 in the CO transceiver.

The CO transceiver also saves its state (step 88 ) in the receiver part state memory 38 , The state preferably includes at least the frequency and time domain equalizer coefficients (FDQ; TDQ and the echo canceller coefficients (ECC) of its receiver and the gain of its transmitter.) The CO transceiver also carries the frame count and superframe count (step 90 ) to ensure synchronicity with the remote CPE transceiver. He can at this time perform his own power or power reduction (step 92 ). In particular, it may reduce or cancel the power or power or energy for the digital modulator / demodulator parts of its transmitter and receiver parts; This provides a significant reduction in power or energy. Power or power is of course maintained for at least the portion of the analog drive circuitry that sends the pilot tone and other control signals to the CPE transceiver.

In response to the acknowledgment from the CO transceiver, the CPE transceiver enters sleep mode or low power mode, respectively (step 94 ), in which a reduced or no power or energy or power is applied to various components of the transceiver. In particular, it stores its state (step 96 ) in the state memory 38 preferably including at least the frequency and time domain equalizer coefficients (FDQ; TDQ and the echo canceller coefficients (ECC) of its receiver part, the gain of its transmitter part and the phase and frequency offset of its phase locked loop 62 , Then he shuts down his transmitter part (step 98 ), including both the digital modulator / demodulator circuits and the analog line driver.

During the sleep mode state, the CO transceiver continues to monitor (step 100 ) the data subscriber line to a "wake-up" signal from the CPE transceiver (step 104 ). The CPE transceiver sends this signal when its controller issues a "wake-up" command (step 102 ) is received from an external source, such as a computer in which it is installed, or from other sources, or if its control is the presence of data in the input buffer 18 detected. The CPE transceiver then restores full power or power to its circuits (step 106 ). It also calls its stored state from the state memory 38 off (step 108 ). It can then begin transmitting immediately because it does not need to repeat the initialization previously required to set up required parameters (equalizer coefficients, echo canceller coefficients, gain, phase locked loop phase and frequency offsets, etc.). Prior to this time, of course, and in response to the "wake-up" signal from the CPE transceiver, the CO transceiver has restored its power, power, or energy, restored its state, and is ready to receive.

at the resumption of communication may be desirable to multiple frames (known) Send data before resuming sending user data becomes. This allows the system to verify that the system conditions not changed so significantly have that one reinitialization is required. If the test satisfactory is, then takes place the user data transmission. Otherwise must be a reinitialization accomplished be before the user data transmission takes place.

As mentioned earlier, the transceiver can 10 as an alternative to the CO transceiver. This is preferably achieved by means of a tone sent by the latter to the CPE receiver. In response to this tone, the CPE receiver introduces the 100 - 110 in 2 shown sequence of steps.

Claims (8)

Multicarrier transceiver ( 10 ) capable of a low power sleep mode, comprising: means for storing selected state parameters representing characteristics of a communication channel over which the transceiver 10 ) is operated; Means for reducing the power supply or power or energy for parts of the transceiver ( 10 ) to enter sleep mode with low power or low power mode; Means for restoring power or power or energy to the parts; Means for returning the transceiver ( 10 ) from the sleep mode or low power mode based on the selected state parameters; and means for restoring communication without reinitializing the transceiver ( 10 ). A transceiver according to claim 1, further comprising means for To lead or maintaining a synchronized data frame count. A transceiver according to claim 1 or 2, further comprising a pilot tone that synchronizes with a remote one Transceiver is maintained. Transceiver according to one of the preceding claims, further comprising means for maintaining synchronization between the transceiver ( 10 ) and a remote transceiver. A method of sleeping or power saving for use in a multi-carrier communication environment, comprising the steps of: storing selected state parameters representing characteristics of a communication channel through which a transceiver 10 ) is operated; Reduce power or power or energy for parts of the transceiver ( 10 ) to enter a low power or low power mode of sleep; Restoring power or power or energy to the parts; Return the transceiver ( 10 ) from the sleep mode or low power mode based on the selected state parameters; and restoring communication without reinitializing the transceiver ( 10 ). The method of claim 5, further comprising guiding Maintain a synchronized data frame count. The method of claim 5 or 6, further comprising Using a pilot tone to sync with one maintain remote transceiver. The method of any of claims 5 to 7, further comprising maintaining synchronization between the transceiver ( 10 ) and a remote transceiver.